The smallest structural unit of an organism which is capable of independent functioning, (i.e., it has an independent metabolism and the capacity to reproduce (with a few exceptions within the human body)); it consists of one or more nuclei, cytoplasm, and various internal organelles, all surrounded by a semipermeable plasma cell membrane; it is capable, either independently and alone, or interacting with other related units of performing all the fundamental functions of life; "the unit of life." [All cells have their origin in the primary cell from which the organism was developed.]
